Presently there are a variety of pressure vessels developed for use in various applications, such as those designed to contain gases for use in fuel cells. Fuel cells have been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. One example of a fuel cell is a Proton Exchange Membrane (PEM) fuel cell. In PEM type fuel cells, hydrogen is supplied as a fuel to an anode of the fuel cell and oxygen is supplied as an oxidant to a cathode. Hydrogen is colorless, odorless, burns without producing a visible flame or radiant heat, and is difficult to contain. A common technique for storing hydrogen is in a lightweight, high pressure vessel resistant to punctures.
Traditionally such vessels are divided into four types. A Type I vessel is a metal vessel. A Type II vessel is also a metal vessel, the vessel having an outer composite shell disposed on a cylindrical section thereof. A Type III vessel consists of a liner produced from a metal such as steel and aluminum, for example, and an outer composite shell that encompasses the liner and militates against damage thereto. A Type IV vessel is substantially similar to the Type III vessel, wherein the liner is produced from a plastic. Furthermore, a conceptual Type V vessel may be developed, wherein the vessel is produced from a composite material. Each type of vessel may include a metal boss disposed therein to house a pressure relief device (PRD).
The PRD is in fluid communication with the interior of the vessel and, when actuated, vents the hydrogen in the vessel to decrease the internal pressure therein. A variety of PRD's are known, and can be actuated thermally, by pressure, or by a combination of both. In a fuel cell system, the internal pressure of the vessel rarely builds to beyond containable levels before the structural integrity of the lightweight vessel is compromised. Therefore, a fuel cell has traditionally been fitted with a thermal PRD such as the one disclosed in U.S. Pat. No. 6,006,774, hereby incorporated herein by reference in its entirety.
Typically, when the ambient air reaches a predetermined temperature, the PRD is actuated. However, where vessels are long, remote portions of the vessel insulated from the PRD can be exposed to localized heat sources without causing actuation of the PRD. Exposure to these localized heat sources can result in a rupture of the vessel. Therefore, to actuate the PRD regardless of exposure to the localized heat source, various pipes, conduits, venting lines, and fuses which actuate the PRD have been positioned along the vessel.
One such pipe is disclosed in U.S. Pat. No. 5,848,604. An elongate pressure vessel is disclosed having a single PRD located at one end. The PRD is thermally coupled to a heat pipe. The heat pipe, which extends generally parallel to an axis of the pressure vessel, conducts heat from the localized heat source at the remote location directly to the PRD. The outer casing of the pipe is made from a thermally conductive metal and is lined with a wicking material, which is capable of moving a fluid by capillary action. The inside of the pipe is filled with a vaporizable fluid. When heat is applied to the pipe, the fluid, which has permeated the wicking material, vaporizes and moves through the central core of the pipe, repeatedly condensing and vaporizing as it travels toward the PRD, until it transfers the heat to the PRD and causes the PRD to actuate.
A fuse is disclosed in U.S. Pat. No. 6,382,232. A heat responsive fuse cord is disclosed which is thermally coupled to a PRD. The PRD is in fluid communication with the pressurized contents of a vessel. When ignited, the fuse cord burns to a thermal coupler, transferring the heat to the thermal actuator of the PRD.
Alternatively, multiple PRDs may be positioned at a plurality of locations along a vessel. Each PRD communicates with the interior of the vessel via a common high pressure line extending from the boss.
Since such devices could be damaged or broken during an accident, and multiple PRDs are expensive, it would be desirable to produce a heat pipe wherein the cost thereof is minimized and the reliability thereof is maximized.